Cross talk reduction in pulse multiplex receiver systems



Patented May 22, i951 Nr OFFICE oao'ss TALKnEDUoTIoN 1N.i PULSE MULTIBLEX. RECEIVER srsrrEMs Alexander Frum,`V Far Rockaway, N'. Y., assigner to International Standard Electric Corporation',

New York, N. Y.; a corporation of Delaware g Application November 1o, 1947, serial No. 785,011

8 Claims.

n l' This invention relates to methods and means for suppressing cross-talk between adjacent channels in multiplex channel pulse `modulation communication systems.

In multiplex communication systems the intelligence ofthe respective channels is conveyed inthe, form of pulses which are modulatedV generally. inrespect to their characteristics of time or amplitude. The pulses of the various channels are provided at given rates of occurrences,l one being Aprovided for each` repetitive cycle. These cyclical' pulses of the various channels are interleaved to formr consecutive trains of pulses, the cycle for the various channels forming repetitif/ e 'groups the extent of which depends upon the number of channels used; In order to eiiectively Vut'ilizethe facilities for transmission and reception of" such multiplex channel systems i fairly close spacing of the channel pulses is usually required with the result that due to distortion or broadening ofthe individual pulses cross Y talk diiculties arise since overlapping of a given channel may extend over one or more ofthe adjacent succeeding channel periods.

j VIt 'is anobj'ect of the present invention to providea method and means to substantially reducefthe effect of overlappingy off adjacentv channel' pulses in multi-channel communication systems ofthe type referred to.

It is another object of the invention to reduce the cross-talk between adjacent ysucceeding channel' periods in communication systems of the above'type by confining the acceptance or passage of the signal conveying pulses to limited periods of time in order to improve the ratio of the'energy representing'the intelligence and the energyrepresentmg cross-talk. i

' Inaccordance with certain features of the invention the successive signal pulses, are permitted to pass to the translating channels by means of gatingin sucha way that gated portions thereof" containsubstantially equal contributions of theA overlap or the transient hangover from respective preceding pulses. which are made to cancel each other at least ink part. by combination thereof in phaseopposition.

The above mentioned andA other features and objects of4 the inventionwill become more apparent anditheinvention itself, though not neces:-v sarilydeiined thereby, will be clearly understood by reference to the4 following description of the embodiment ofthe invention taken in connection with the accompanying drawings wherein:

Fig. 1 is a circuit diagram substantially in blocl: form indicating a receiver of. a system in accordance with the invention; and a Fig. 2 is a series of graphs illustrating certain operative conditions of the system ofFig- 1.

Referring now to the diagram in Fig. 1, the refierence I shows a receiving circuit, wherefrom is obtained a train of pulses representing the various communicating channels of a multiplex pulse modulating system. The train of pulses as is generally the case, includes` periodically occurring synchronizing or marker pulses which are selected or isolated in av marker pulse selector circuit 2. These synchronising. pulses are utilized vfor controlling a sweep generator circuit 3 which controls the cyclical deflection of a cathode ray beam across targets` l ina catho-de ray type distributor 5 which acts tok periodically connect. the respective channels 6 in synchronism with the incoming signal pulses. The cathode ray distributor 5 is of a well known type and includes an electron gun comprising a cathode l, control grid 8 and deection plates 9 and itl respectively.. An aperture. plate II in front of the targets It. forms a so-called dynode secondary electron emis sion system in conjunction withA these targets as. disclosed in the prior art. The train of pulsesr from the receiver is applied simuitaneousiy to-a. pair ofF gated amplifiers indicated atl i2 and i3; which are controlledl from a gate pulse generator circuit I4- supplying suitable gating pulses-L The isolated synchronizing pulse from. the marker selector 2 are applied to a pulse multiplier circuitv I5 wlherebvA each of theV synchronizing pulses is' caused tov provide anumber of pulses occurringsubstantially in sychronism with the respective channel pulses.

Theseseries of multiplexed pulses are applied to a triggering device I6 which may be differentator or similar device to provide narrow type, high energy pulses in order to effectively trigger the gate pulse generator I4 which may take the form of a multivibrator for supplying square pulsesv having positive and negative polarity or phase, respectively. The timing or phase relationship `and amplitude. of the square pulses obtainedv from the generator I4" may be adjusted .by suitable adjustment means in the triggering circuit I6 and the generator I4 itself respectively. .As the successive signal or channel pulses are applied to the gated amplifiers I2'.and I3, the gating pulses synchronously applied thereto permit selected portions of these pulses to pass through the ampliers I2 and I3 which portions are combined at point I1 after one of the portions has been inverted in phase in a suitable reversing circuit I8 and the other portion has been appropriately delayed in delay device Ia. The combined resultant signal is applied as a control voltage to the control grid 8 whereby the cathode ray beam is effective only during the application of such resultant signal portions. Although the gating pulses have been described as being positive and negative, this'is merely a convenient way of selecting the pulses for use in the separate gated amplifiers. It will be understood that any characteristic which will permit the segregation may be used. V Y

Referring now to the graphs of Fig. 2 the successive channel pulses are indicated at I9 and each of them shown to have overlapping portions indicated at 2| and E2 from preceding channels. The resulting overlap, that is, the area of a hangover of a preceding pulse coincidental with the signal area of the succeeding pulse is shown in cross-hatch (graph a). In graph b are shown the type of gating pulses obtained from the generator Ili the positive and negative portions being indicated at 23 and 2d respectively and occurring simultaneously with the main channel pulses. The cross-hatched portions of the gating pulses indicated in graphs c and d indicate the main signal portions and cross-talk portions of the pulse energy admitted or passed through the gate amplifiers I2 and I3.

As the positive and negative gate-passed portions shown in graph c are combined, the portions shown in graph d which are due to crosstalk, effectively cancel each other out to a substantial degree, while the remaining signal portion is effective in conveying the intelligence transmitted and becomes substantially free of cross-talk or channel interference.

This method is particularly eiective with pulses which are amplitude modulated and Where the trailing edges of the transient or overlapping hangovers are not oscillatory. In the form shown the positive peak of the gate pulse is phased such that it admits the maximum portion of the desired pulses, the negative peak being so placed that it passes a section or" the desired pulses substantially adjacent to the maximum portions but perhaps 6-10 db down. Assuming that the hangover of the preceding channel is fairly smooth and level, the cross-talk contributions passed by the two gating pulses will be substantially equal and will cancel each other while the main signal will not be weakened to a similar degree. The present invention has been described particularly in combination with a receiving circuit, as certain advantages are obtained thereby. It is however comtemplated not to limit the application to the receiving end but leave the application of the cross-talk suppression system open to practical consideration, the transmitter end being quite suitable at certain times.

While I have described the principles of my invention in connection with speciiic apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of my invention.

What is claimed is:

1. A circuit for reducing interchannel interference in a multi-channel pulse modulation communication system having channel pulses which form a train of interleaved pulses representing individual channels conveying intelligence, the said pulses having undesired portions overlapping into succeeding pulses and occurring at a predetermined rate of repetition, comprising means for generating a pair of gating pulses synchronously with two parts of each of said channel pulses, theV undesired -overlapping portion having substantially equal values, while the channel pulse has substantially diierent values, at said two parts, means for distributing said channel pulses to a plurality of corresponding channels, means operatively controlled by said gating 'pulses for controlling by gating the application of said channel pulses to said distributing means, and means for combining the two gated Yparts of each channel pulse at the output of said controlling means in phase opposition, whereby the gate-passed pulse portions of theoverlap are substantially eliminated and a representative portion of the channel pulses is obtained.

' 2. A circuit according to claim 1, wherein said distributing means comprises a cathode ray electronic distributor.

3. A receiver circuit for reducing interchannel interference in a multi-channel pulse modulation communication system having channel pulses which iorm a train of interleaved pulses representing individual channels conveying intelligence, the said pulses having undesired portions overlapping into succeeding pulses and occurring at a predetermined rate of repetition,V comprising means for receiving the train of channel pulses, means for deriving from said received p-ulse train a signal representative of the rate of repetition of said pulses, means energized from said deriving means for generating a pair of gating pulses synchronously with two parts of each of said channel pulses, the undesired overlapping portion having substantially equal values, while the channel pulse has substantially dierent values, at said two parts, a pair of gating amplifiers operatively connected to said receiving means and operatively controlled by said gating pulses respectively, means for additively combining the two gated parts of each channel pulse at the output of said pair of ampliiiers in phase opposition, a plurality of communication channels for utilizing said received channel pulses, and a cathode ray electronic distributor intermediate said combining means and said communication channels, the channel pulse portions passed by said gating ampliers controlling said distributor.

4. A circuit according to claim 3, wherein said deriving means comprises means for selecting synchronizing pulses from said pulse train.

5. A circuit according `to claim 3, wherein said combining means includes a pulse phase reversing device associated with one of said ampliiiers.'

6, A circuit according to claim 3, wherein said deriving means comprises means for selecting synchronizing pulses from said ypulse train, and saidV generating'means includes a multiplier energized from said synchronizing pulse selector, a trigger circuit and a gate pulse generator.

7. A circuit according to claim 6, further including adjusting means for said trigger circuit and said gate pulse generator for adjusting the 5 phase and amplitude respectively of said pair of gate pulses.

8. A circuit according to claim 3, wherein said deriving means comprises means for selecting synchronizing pulses from said pulse train, further including a sweep voltage generator for said electronic distributor operatively controlled from said selecting means.

\ ALEXANDER FRUM.

REFERENCES CITED The following references are of record in the 111e of this patent:

Number in Number 6 UNITED STATES PATENTS Name Date Gloess Mar. 25, 1941 Wolf Dec. 4, 1941 Hansell Feb. 9, 1943 Blurnlein Feb. 16, 1943 Bingley Apr. 3, 1945 FOREIGN PATENTS Country Date Great Britain J'uly 16, 1948 

